Either "she is cutting some bread" was just "another correct answer" suggested by Duo, or you made a mistake in writing "she is cutting bread", since both translations are duly registered in the system.

Your question has already been answered if you would kindly read through the forum. Your translation of the verb is not the problem; the problem is translating "the". « Du pain » is an undefined quantity of a mass of bread, which can be translated as "some bread" or just "bread". « Le pain » is "the bread".